1. Field of the Invention
The present invention relates to a hydraulic operating device, in particular for the operation of a selector fork of a gearbox, comprising a double-acting cylinder, a pump, and a reservoir for hydraulic fluid.
2. Description of the Related Art
A hydraulic operating device for the operation of a selector fork of a gearbox is known. This known device comprises a single-acting electrically driven pump, the suction port of which is connected to the reservoir and the pressure port is connected, according to choice, via an electrically operated valve to one of the two working chambers of the double-acting cylinder. The working chamber which is not connected to the pump is then connected to the reservoir. The valve has a non-operating position in which both working chambers of the double-acting cylinder are connected to the reservoir.
For the effecting of a fast movement of the selector fork, the pump, which has a high output, is switched on for a short period, whilst at the same moment the valve is operated and this connects the pressure port of the pump to the desired operating chamber. As soon as the pump is switched off, operation of the valve is discontinued such that this valve again takes up its non-operating position. It is important that this device ensures that the double-acting cylinder is now "pressureless", that is that there is no residual pressure remaining in the cylinder which would continue to load the selector fork. This would in practice lead to excessive loading and wear of the synchronizing rings normally present in a gearbox.
The known device has the disadvantage that the use of the electrical valve leads to an undesirably high cost.